压弯载荷下焊趾表面裂纹工程萌生寿命预测

首先定义焊趾处从无裂纹到检测到表面裂纹长度达到 1.5mm时对应的循环次数为裂纹“工程萌生寿命”。给出了基于修正Neuber法并考虑焊接残余应力等影响的焊接结构焊趾裂纹工程萌生寿命计算方法。用成一定角度对接焊板试件和轴向加载获得压弯组合应力 ,以 980钢板焊接件为试件 ,在压弯组合应力的作用下 ,对焊趾表面裂纹萌生寿命进行了实验研究 ,确定了焊趾处的疲劳缺口系数。该结果可用于疲劳热点部位的受力特征为压弯组合应力的潜艇耐压壳、压力容器等的某些重要焊接结构疲劳计算     

Effectiveness of coir-based rolled erosion control systems in reducing sediment transport from hillslopes

Accelerated soil erosion is ubiquitous on human-modified hillslopes. A variety of erosion control products have been developed to reduce on-site soil resource degradation, and off-site transport of sediment and sediment-associated contaminants to receiving water bodies. However, limited quantitative data are available to assess erosion reduction effectiveness, and to establish the salient properties of the erosion control products. A replicated field-based rainfall simulation study was conducted to compare the runoff and erosion effectiveness of three coir (coconut) fiber rolled erosion control systems (RECSs) with a bare (control) treatment. Detailed temporal measurements of runoff and sediment transport were made during two phases of each experiment: (1) a 110-min application of rainfall via a rainfall simulator at 35 mm h⁻¹ after runoff initiation and (2) a 30-min period, at 3 times the flow rate of phase 1, applied via an overland flow generator. All coir treatments enhanced infiltration, delayed time to runoff generation, reduced intensity of rill incision, and reduced sediment output compared to bare treatments. More importantly, statistically significant differences were observed between coir RECSs of different architecture. For the two open weave coir systems tested, the most effective design had a higher mass per area, and less open space between the regularly aligned grid of fibers. The random fiber coir architecture was the most effective, having significantly lower runoff sediment concentrations, lower sediment yields, and a lower frequency of rill initiation. The differences in system architecture are examined in light of fundamental controls on runoff and erosion processes.     

俯冲初始时板块分界面形状对俯冲过程的影响

自板块理论建立以来,俯冲一直是学者们关心的热点问题.前人结合地质、地球物理、实验室物理实验和数值模拟等多种手段对这一问题进行了大量的研究.以往的研究更为关注俯冲过程中板块的作用、地幔流动的规律和物质的迁移与相变等问题,却常忽视了俯冲是如何开始的这一基本问题.同时,由于相关数据资料较为有限,更限制了俯冲启动的相关研究.因此,本文选取俯冲启动问题中板块分界面形状对俯冲过程的影响这一问题,使用有限元的方法进行了数值模拟.我们选择针对倾斜型、垂直型和弯曲型三种不同形状的板块分界面建立对比模型,比较它们演化至10 Ma的过程我们发现：分界面几何形状的不同的确会对俯冲板块演化和海沟的深度产生影响.倾斜型模型的俯冲角度最大,海沟深度最深,俯冲深度最深;垂直型模型的俯冲角度和海沟深度仅次于倾斜型模型,俯冲深度最浅;弯曲型模型的俯冲角度最小,海沟深度最小,俯冲的深度介于倾斜型和垂直型之间.结合以上结论不难看出,俯冲角和海沟深度变化具有一定的相关性,俯冲角度越大,相应的海沟深度越大.

     

Geomorphological characteristics of small debris flows on Junior's Kop,Marion Island,maritime sub ‐ Antarctic

The geomorphological characteristics of small debris flows in a maritime sub‐Antarctic environment are described. The morphological and sedimentological characteristics of the debris flows are comparable to debris flows documented for other parts of the world; their initiation appears closely linked to the unusual environment in which they are found. Sediment supply is generated by diurnal frost heave of loamy sediment associated with Azorella selago. The debris flows are triggered by sediment mobilization upon saturation of the frost‐heaved surface gravel and overland flow over the low‐permeability and frost‐susceptible slope materials. Morphological effects of the flows are short‐lived due to obliteration by subsequent frost heave activity. Copyright © 2000 John Wiley & Sons, Ltd.     

INVESTIGATION OF INFILTRATION CHARACTERISTICS AND DEBRIS FLOW INITIATION CONDITIONS IN DEBRIS FLOW SOURCE AREAS USING A RAINFALL SIMULATOR

Rainfall was simulated on unconfined plots on regolith in debris flow source areas using a portable simulator. In total, 351 simulations were carried out on steep slopes (27–54°) with rainfall intensities of 28–291 mm/h. From these rainfall simulations the infiltration parameters sorptivity (S) and steady-state infiltration capacity (K) of the regolith, and a threshold for the occurrence of micro-scale mass movements, were obtained. Two evaluation methods were used to obtain the infiltration parameters K and S. The ‘infiltration envelope’ method uses rainfall intensity and time to ponding from multiple tests and fits an infiltration envelope through the data from which K and S can be obtained. The ‘constant runoff’ method uses rainfall intensity and overland flow intensity to calculate K, after which S can be calculated in several ways by using time to ponding. The constant runoff method produced K values of 16.6–128 mm/h, which usually show a log-normal distribution. K values depend on the regolith parent material and rainfall intensity. Using this method, S values are 0.088–0.381 cm/min^1/2. The infiltration envelope method produced K values of 9.8–131 mm/h and S values of 0.14–0.32 cm/min^1/2. It can be argued that both methods overestimate K as well as S, but quantitative relations between measured/calculated and actual values of K and S have not yet been obtained. At high rainfall intensities, typically 100 mm/h or more, micro-scale mass movements sometimes occur. A lower threshold curve for the occurrence of these micro-scale mass movements has been constructed. It is a function of both slope angle and rainfall intensity. The micro-scale mass movements could play an important part in the initiation of debris flows in the study area, possibly by delivering sediment to overland flow. On the very steep slopes, the sediment-rich overland flow can easily mobilize coarse material.     

鲜水河-安宁河断裂带深部构造特征、固体潮应力变化与地震触发相关性研究

本研究通过反演241,561条纵波和209,363条横波高质量的地震走时数据,获得了鲜水河、安宁河断裂带的P波、S波以及泊松比的三维结构模型,并结合相位分析与Schuster测试讨论了该断裂带上地震事件的触发与其深部构造以及固体潮所产生的应力变化三者之间的关系.结果表明,鲜水河—安宁河断裂带26.5°N、28°N、29.5°N以及31.5°N四个位置附近存在低速、高泊松比异常,可能暗示着深部流体（包括部分熔融物质）的上涌.这些大范围分布的流体提高了孕震层的孔隙流体压力,削弱了断层面之间摩擦力,在鲜水河—安宁河断裂带形成了一些具有高度地震活动性的区域.此外,相位分析与Schuster测试的结果表明,鲜水河—安宁河断裂带附近的地震触发与固体潮剪切应力的变化密切相关.综合分析的结果表明,固体潮与构造应力对地震触发可能存在某种"合"的关系.在分布着大量流体的区域,地震事件可能对固体潮更加敏感.     

Dating basal peat: The geochronology of peat initiation revisited

Attributing the start of peat growth to an absolute timescale requires dating the bottom of peat deposits overlying mineral sediment, often called the basal peat. Peat initiation is reflected in the stratigraphy as a gradual transition from mineral sediment to increasingly organic material, up to where it is called peat. So far, varying criteria have been used to define basal peat, resulting in divergent approaches to date peat initiation. The lack of a universally applicable and quantitative definition, combined with multiple concerns that have been raised previously regarding the radiocarbon dating of peat, may result in apparent ages that are either too old or too young for the timing of peat initiation. Here, we aim to formulate updated recommendations for dating peat initiation. We provide a conceptual framework that supports the use of the organic matter (OM) gradient for a quantitative and reproducible definition of the mineral-to-peat transition (i.e., the stratigraphical range reflecting the timespan of the peat initiation process) and the layer defined as basal peat (i.e., the stratigraphical layer that is defined as the bottom of a peat deposit). Selection of dating samples is often challenging due to poor preservation of plant macrofossils in basal peat, and the representativity of humic and humin dates for the age of basal peat is uncertain. We therefore analyse the mineral-to-peat transition based on three highly detailed sequences of radiocarbon dates, including dates of plant macrofossils and the humic and humin fractions obtained from bulk samples. Our case study peatland in the Netherlands currently harbours a bog vegetation, but biostratigraphical analyses show that during peat initiation the vegetation was mesotrophic. Results show that plant macrofossils provide the most accurate age in the mineral-to-peat transition and are therefore recommendable to use for ¹⁴C dating basal peat. If these are unattainable, the humic fraction provides the best alternative and is interpreted as a terminus-ante-quem for peat initiation. The potential large age difference between dates of plant macrofossils and humic or humin dates (up to ∼1700 years between macrofossil and humic ages, and with even larger differences for humins) suggests that studies reusing existing bulk dates of basal peat should take great care in data interpretation. The potentially long timespan of the peat initiation process (with medians of ∼1000, ∼1300 and ∼1500 years within our case study peatland) demonstrates that choices regarding sampling size and resolution need to be well substantiated. We summarise our findings as a set of recommendations for dating basal peats, and advocate the widespread use of OM determination to obtain a low-cost, quantitative and reproducible definition of basal peat that eases intercomparison of studies.     

硬岩裂纹起裂强度和损伤强度取值方法探讨

岩石裂纹起裂强度σci和损伤强度σcd的研究对探讨岩石渐进破坏过程和脆性破坏机制,建立岩石的起裂强度和长期强度准则具有重要意义。鉴于此,系统总结了岩石起裂强度和损伤强度的4种计算方法,包括裂纹应变模型计算法,声发射参数取值法,侧向应变、体积应变曲线观察法和移动点回归法,并以大理岩和花岗岩在单轴压缩条件下为例,详细描述了用不同方法计算σci和σcd时存在的问题。研究结果表明,裂纹应变模型法物理意义明确,可以方便和准确地确定岩石的σci和σcd;声发射撞击率可以定性或半定量了解岩石的渐进破坏和损伤过程,但无法准确定量确定σci和σcd;移动点回归法计算体积应变刚度时受取值点间隔影响较大,而且加载过程中不同阶段的特征并不明显,难以确定起裂强度值。研究结论可为加深对岩石裂纹起裂强度和损伤强度的重要意义的认识,了解两个强度值的计算方法并合理选取其计算方法提供有益的参考。     

Migration of channel heads following wildfire in the Colorado Front Range,USA

The High Park Fire burned ~35 300 ha of the Colorado Front Range during June and July 2012. In the areas of most severe burn, all trees were killed and the litter and duff layers of soil were completely removed. Post‐fire erosion caused channel heads to develop well upslope from pre‐fire locations. The locations of 50 channel heads in two burned catchments were documented and the range of drainage areas contributing to these channel heads to drainage areas of unburned channel heads in the region measured previously were compared. Mean drainage area above channel heads in the burned zone decreased by more than two‐orders of magnitude relative to unburned sites. Drainage area above channel heads between the two burned catchments does not differ significantly with respect to slope, likely as a result of differences in surface roughness between the two sites following the fire. Copyright © 2013 John Wiley & Sons, Ltd.     

Climate‐invariant area–slope relations in channel heads initiated by surface runoff

We use a dataset of 38 field‐mapped channel heads from a semi‐arid environment in western Colorado to examine relationships between contributing drainage area (A) and local hillslope gradient (θ) in relation to dominant process of initiation (surface runoff versus subsurface flow). Channel heads resulting primarily from subsurface flow have significantly greater values of A, longer basin lengths, and shallower local gradients than channel heads resulting primarily from surface runoff. We also compare the data from western Colorado to six analogous datasets from more humid regions in other portions of the United States and in southeast Australia. Comparison of the confidence intervals for the exponent values of A–θ regression lines reveals that the confidence intervals for the exponent of western Colorado channel heads with both surface and subsurface flow overlap with the confidence intervals for the exponent of all other datasets. This suggests that A–θ relationships do not differ significantly between diverse geographic locations. Copyright © 2017 John Wiley & Sons, Ltd.